Heating unit for heat transfer liquid



Feb. 9, 1960 F. A. Lol-:BEL

HEATING UNIT FOR HEAT TRANSFER LIQUID Filed Nov. 17, 1954 Nm, EQ.

United States Patent 2,924,203 HEATING UNIT FOR HEAT TRANSFER LIQUIDFrederick A. Loebel, Milwaukee, Wis., assignor to Cleaver-BrooksCompany, a corporation of Wisconsm Application November 17, 1954, SerialNo. 469,341 3 Claims. (Cl. 122-149) is ordinarily desirable to employ aslittle heat input as y possible to the transfer liquid to effect adesired heating of the product. Time is also usually a governing factoras ordinarily the heating should be accomplished quickly in order toavoid unnecessary delays.

2,924,203 Fatented Feb. 9, 1960 ice? 2 to the embodiment illustrated.The scope of the inventionvwill be pointed out in the appended claims.

The present invention, in general, provides a heating unit to which acoil and suitable lines will be attached to form, with the liquid spacein the heater, a closed circuit for circulation of heat transfer liquid.The pres- The present invention is concerned with an improved heatingunit for raising the temperature of a heat transfer liquid andcirculating it into and out of the heater in a closed circuit. Thepresent unit has several advantages which have not been present inexisting units for the same purposes. t The structure is so arrangedthat all of the heating surfaces of the furnace have thetransmaintaining a minimum differential between the temperatures of theheated surfaces and the transfer liquid. Diflculties of expansion andcontraction of the furnace parts are avoided since, in effect, thefurnace structure is full floating and at the sarne time permittingready removal of the furnace for cleaning.

A further advantage of the new structure is that it permits a minimumquantity of liquid in the heater thus reducing the cost.

It is, therefore, the principal object of this invention to provide anew and improved heating unit of the character described.

Another object is to provide a heating unit for heat transfer liquid inwhich the liquid may be passed at high uniform velocity in contact withsubstantially all of the heated surfaces of the unit.

A further object is to provide a heating unit of particularly higheiciency coupled with a low operating cost.

Other features, advantages and objects of the present invention will beapparent from the following description of a preferred embodimentillustrated in the accompanying drawings in which:

Figure 1 is a side elevational view, partly in section, of the improvedheating unit of this invention;

Figure 2 is a vertical sectional view taken through the heating unitsubstantially along line 2 2 in Figure l; and

Figure 3 is a vertical sectional view taken through the heating unitsubstantially along line 3 3 in Figure l.

fer liquid pumped thereover at a uniform high velocity ent invention isconcerned with the heating unit, its structure and mode of operation. Inthe past, boiler type constructions, in Iwhich a number of fire tubessecured at Iopposite ends in tube sheets, have been used within a shellfor the passage of combustion products which heat the transfer liquid inan out-of-contact heat exchange relation. Diiculties have beenencountered since the transferliquid did not come in contact with all ofthe heated surfaces in a uniform manner, thus permitting parts of thefurnace to be at much higher temperatures than other parts. Some partsof the furnace were stressed to such a degree that an actual pullingloose of the parts sometimes occurred.

In the present structure, the furnace extends into the shell of theheater in a manner allowing expansion and contraction of the furnaceWithout danger of the breakage of any of the parts. At the same time,the structure is so arranged that the heating liquid is pumped over thefurnace structure at a very high velocity compared with what has beenpossible in the past. This results in a very small differential intemperature between'the heated surfaces and the liquid. Uniformity inthe expansion and contraction of the furnace parts is also achieved bythis structure.

The unit is intended for use in the field so that it is ordinarilymounted on skids 4 forming the base for sup-l porting the shell 5 aboutwhich an insulating layer of material 6 is placed and covered by aretaining sheet metal cover 7. The heater ordinarily operates atatmospheric pressure and an expansion tank or space is provided tomaintain the pressure at atmospheric pressure. The shell is providedwith a flange 8 at one end and a dome-shaped or spherical end 9 oppositethe flange. The front of the unit mounts a burner structure generallyindicated l0 which includes the burner 11, anda motor 12 for operating ablower inside an air plenum cham.- ber 13 having an air intake at 14.The burner structure 10 is generally the same as disclosed in theapplication of Cleaver et al., Serial No. 403,286 tiled January l1,1954, now Patent No. 2,835,230.

This burner structure is mounted on a door which is hinged to acombustion products gas chamber 15 directly The products of combustionformed in the burner 11 are discharged into a burner section 16 so thatthe flame may travel down the main re tube 17 of the furnace toward thespherical end 18 thereof. At the end of the main re tube 17, thecombustion products enter one or an other of a plurality of return ues19, each of which has an end portion 20 communicating through an openingwith the interior of the main fire tube. The return fiues are eachhelically wound about the tire tube and communicate at the burner endwith the chamber 15 and stack 21. For instance, the particular returnilue connecting with the fire tube on the near side of the same, asillustrated in Figure 1, has its exit into the combustion productschamber at 22. The return flues are generally wound in parallel lines sothat in a sense the live ilues are in the form of a compound thread. Forthe particular size of fire tube and flues illustrated, each flue makesabout While this invention is susceptible of embodiments in manydifferent forms, there is shown n the drawings and is herein describedin detail one specific embodiment, with the understanding that thepresent disclosure is to be considered as an exemplcation of theprinciples 0f the invention and is not intended to limit the inventiontwo and three-quarters turns about the tire tube.

The particular form of the furnace or heating element is advantageous inthat it permits expansion and contraction of the tire tubes and ueswithout the danger of breaking any of the connections. The productschamber 15, tire tubes and ilues are all supported by a heavy ange i2,924,203 p q i y f- 23 secured to the flange 8 of the shell and areextended thereby in a cantilever fashion into the shell. This Apermitsready removal for cleaning which must be done from time to time as theformation of coke is dependent upon a time-temperature relationship.

The heattransfer liquid `is conducted :into and Yout `o'f the :shell.through an inlet 25 and anioutlet 26. V.I'he space within the shellabout the furnace forms a part :of .aclosed circuit with a coil ofpipelines which may be `connected with the inlet and outlet."Ordinarily, a circulating pump is connected `to .the outlet 26 forforcing the heated Voil or other liquid through heat transferequipmentsuch asstorage tanks, heating :coils or other heat exchangers.

,Theiform of the present heater employs a shroud '.27 `of generallycylindrical form `placed in 1the shell and :about the-.tire tube Yand'flues concentrically. Spacers '28 vserve to "hold .the shroudtinposition. The end of the ,shroud adjacent .the `stack 21 is open while`the other end has a partially spherical end `29 with a neck portion 30forming a `central opening. The shroud thus divides the interior of `theshell into a return passage between itself and the shell and a heatingpassage between the shroud and the fire tube. The transfer liquid isheated passing over `the furnace surface after which `is passes aroundthegend vof thelshroud to the-outlet 26. Cold Lliquid vis draw-n backinto the shell through the inlet 2S while at thefs'ame time some oil maybe by-'passed around the outsideV of the shroud to-again pass to theheatingzone. Spacer Iinembers 31 are also employed to `space the Vshroud`around the tire tube. i

'One of-Ytheimportant features of thel present invention is'theAstructure by which the transfer'liquid Yis forced foyer the heatedsurfaces -at a uniform `high velocit-y.A

maintains the heated surfaces at a lower temperature-than otherwisewould be possible. ln the 4present invention, a propeller 40 "is mountedon Ya shaft in the end foftheshell so that iit rests withinithereducedportiox1i30=of`th`e shroud and-is positionedfbetweenfthe passagesmentioned. A suitablernotor 441 is providedgwith a belt 42 fordrivingthe propeller. Cold oilmay pass from lthe linletthrough louversi143 :to the blades of the propeller '40 and 'is -then forcedlongitudinally over the re tube aad return flues. The propeller `turnsin the direction of the-'windingiof -theV ilues so that the oil mayfollow a path slightly helical in nature `rather than strictlylongitudinally of the 's'hell. This structure .contributes to a very'lowyhead 'loss which has `vbeen experiencedywith theunit.

The primary benet of the pumping arrangement just described is themaintenance of a relatively highyelocity of ow of the transfer 'liquidover-the-heated surfaces. it has been found that velocities 4of theorder 'of seven to eight feet per-second may 1be=maintained withoutrequiring especially large driving motors foithe propeller. At suchf-velocities, a temperature differential Vbetween the heated 'surfacesvand the liquid of not substantiallymore than 570 :F.have beenrachieved.The-shroudis placed quite close to the return ues -so that a generallyuniform, relatively thin passage is providedforthe liquid over theheated'surfaces. There is practically no obstruction in the pathof theliquid throughthisuniformsize channel. The fact thatltheremay be morespace betweenthe `shroud and the flire tube in between the flues'does'not interferelwith heated surfaces of the furnace to the transferliquid. Gas .temperaturesfin .the -inlets to the -return `ilues havebeen found in the range of l500 to 1850 F. whereas the metaltemperatures close to the same locations would be under 500 and in somecases below 400 1F. The gas in the stack would generally run no morethan 200 F. higher than the metal temperatures. lt was found that whenthe propeller pump 40 was stopped the heated surfaces would ,rise -in:temperature quite Lrapidly and would accordingly .as rapidly be brought,down in temperature once l:the -pump `.wasreturned toguse The structureof the present invention is intended for longservice `of a very eicientnature. It may be easily serviced since the furnace 'may Aibe removedfrom the shell quite readily.

Safety features `are employed by the use of a pop-olf pressure valve44and a blow-out plug 45. To accommodate any expansion in the heatedtransfer fluid, a line 46 communicating with the space within the shellmay be connected tosan expansion tank.`

' 4iiIlt-:laim: i

1. A- heating unit'for heat transfer liquid subject tofde'- compositionby .applicationfof heat, comprising: an elongatedxshelli; Y`a'heatinguelement secured only to one end t ofth'eish'ellwand'Y having 'agenerally cylindrical nfire tube and'iretiiiinfliuescantileveredintoi'the she1l,"isaid return nues l:beinggenerally lhelicali and Woundabout the lire tubeglanope'n-ended.shroud closely spaced about the retubeianti lluesforming `a narrow liquid passage over fthe i tire tuberandiue surfaces; .a circulating pump impeller i mounted in#thexotheriend ofthe shell and arranged to` force `iliquid V.throughsaid liquid lpassage at generally 'unif for'm velocity over alltheheated surfacesof there tube andireturn ues, said pump impeller forcingthe `transfer t liquid, in vthe direction of the helical path 'of thezretum ues Zso as to minimize `head lloss in the liquid passage;

and aftransferliquid inlet in the ishell adjacent l'thepumpu andanoutlet in the'shell `spaced from saidinlet.

2. -A heating unit for `heat transfer liquid subject lto decompositionby application of heat,` comprising:` an

elongated shell; a heating element Isecured only lto one endlof ltheshell and `having a re tubey and return ilues cantilevered into `theshell; an open-ended `shroud suff ciently closely spaced about the tiretubeand flues to Iform a narrow liquid passage bounded 'bythe-shroudireftube andiiue surfaces; a circulating pump-impeller mounted in theother end of the shell and arranged *to -force liquid through saidliquid passage at generally uniform Avelocity overall the 'heatedsurfaces of the re tube and `return nues; and a transfer liquid imeiinthe sheuaaiceniihe thei-uniformow. Thus,-"theshroud is placed quiteclose pump and an outletin thezshellzspaced from said inlet.

'-3. A vheating `unit for heat transfer `o'il `toibe kcirculated throughcoils, lines and the like, comprising: a base; a heating shell mountedupon `the base y,andkhaving a transfer oil inlet `and an outlet therein;a heating, element L secured-to one end of the'shell and having:ah'portion extending into said heating `shell in cantiIeVeraSh'iQn,said heating unit including an inwardly extendingire tubeand a pluralityofreturn ilues Iarranged about'the Afire tube in helical pattern forconducting flue gases out of the shell; an `open-,ended "shroud,surrounding the 'helical ues in suilcien'tly closely spaced relationthereto .as to `form helioal passages'therewith, said shroudfbeingspaced from theA shell andhaving a portion of diminished :size aboutthefree end of the furnace, saidtransferoil inlet and outletcommunicating. with a space within the shell about the shroud; anda.,c`i rculating pump impellenmounted in saiddiminished sizeportion ofthe shroud for forcing t transferroil from the; spaceoutside `-theshroud `over the lengthof the Ifurnace ,-in `the direction of ,the-helical passag=S.,` Said shroudv having a portion aboutthe flues;forming an' annularelongated passage-for the liquid-substantallyVufnizihstructed permitting @relatively t uniform high v'elocityidw overthe tube and'llue surfaces.

(Re'ferences on rfllowingtpage) i UNITED STATES PATENTS Maxim Nov. 1,1910 Prache Feb. 17, 1920 Schwarz June 24, 1930 Howard Feb. 10, 1931Morgan Nov. 13, 1934 Gallagher July 2, 1935 Derby Oct. 8, 1940 AldridgeNov. 18, 1941 6 Brantly Aug. 4, 1942 Nelson Dec. 11, 1951 Glasgow et al.Jan. 20, 1953 Ray Oct. 27, 1953 Lustig Mar. 8, 1955 Putney July 23, 1957FOREIGN PATENTS Germany uly 26, 1904 Great Britain Nov. 10, 1932

